MIPS: MT: Fix build with CONFIG_UIDGID_STRICT_TYPE_CHECKS=y

MIPS: MT: Fix build with CONFIG_UIDGID_STRICT_TYPE_CHECKS=y

When CONFIG_UIDGID_STRICT_TYPE_CHECKS is enabled, plain integer checking
between different uids/gids is explicitely turned into a build failure
by making the k{uid,gid}_t types a structure containing a value:

arch/mips/kernel/mips-mt-fpaff.c: In function 'check_same_owner':
arch/mips/kernel/mips-mt-fpaff.c:53:22: error: invalid operands to
binary == (have 'kuid_t' and 'kuid_t')
arch/mips/kernel/mips-mt-fpaff.c:54:15: error: invalid operands to
binary == (have 'kuid_t' and 'kuid_t')

In order to ensure proper comparison between uids, using the helper
function uid_eq() which performs the right thing whenever this config
option is turned on or off.

Signed-off-by: Florian Fainelli <florian@openwrt.org>
Patchwork: https://patchwork.linux-mips.org/patch/4717/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>